Proposed mechanism: Intravascular hemolysis increases free plasma hemoglobin and arginase, which results in reduced blood nitric oxide (NO). The state of reduced NO bioavailability results in impaired blood flow.
Features of hemolysis-associated endothelial dysfunction:
(1) priapism
(2) leg ulceration
(3) pulmonary hypertension
(4) increased mortality
Markers of intravascular hemolysis:
(1) steady state serum LDH > (mean for the normal range) + (1 standard deviation)
(2) steady state serum AST > serum ALT
(3) anemia with increased reticulocytes
(4) elevated plasma hemoglobin and bilirubin, decreased haptoglobin
(5) low transcutaneous oxygen saturation
where:
• The mean for serum LDH is: ((upper limit for reference range) + (lower limit)) / 2.
• The standard deviation for serum LDH with normal range +/- 2 SD is: ((upper limit for reference range) - (lower limit)) / 4
• The cutoff for LDH above is therefore: ((3 * (upper limit)) + (lower limit)) / 4
• The abnormal laboratory values are steady state values associated with ongoing intravascular hemolysis. This is distinct from the hyperhemolysis that occurs during vaso-occlusive pain crisis (VOC).
